Tools are devices used to perform or facilitate mechanical work. The term “tool” may be used to denote the entire instrument (such as a hammer or screwdriver) or only a portion of the instrument (such as a cutting or shaping part in a machine or machine tool). Tools typically are used to perform some action on a “work piece,” such as a piece of wood, metal, or plastic, and may be used alone and/or in conjunction with a worktable or workbench used to support the work piece and/or tool.
Drill presses are exemplary tools used mainly for producing or modifying holes in a work piece. These work pieces most commonly are positioned by marking the work piece with the center location of a desired drill hole. The work piece is then placed under the cutting tool and moved around on the table until the center of the tool corresponds with the mark. The work piece may then be clamped to the table for drilling. Unfortunately, this method suffers from two significant drawbacks. The first drawback is that it is hard to position the work piece accurately under the tool. This is increasingly more difficult with large drills. In particular, as drills increase in diameter, the web or center of the drill typically increases in size making it harder to estimate the true centerline of the tool. The second drawback is that clamping work pieces of various sizes can be cumbersome, time consuming, and/or the cause of further errors in work piece positioning.
Several drill press positioning systems are available on the market. These systems range from simple stopping fence arrangements, such as that shown in U.S. Pat. No. 3,185,470, issued Jul. 30, 1963, to systems that incorporate a flat table with a calibrated fence and stop in two planes, such as the Incra Drill Press Table. The simple stopping fence arrangements have no real measurement functions, acting only as a support during drilling, and a reference for subsequent parts that are to be drilled at the same location. The Incra table requires accurate tracks in the table to guide the fence with as little play as possible as it is moved into different positions.
Some of the shortcomings in the positioning systems discussed above are addressed by the drill press table shown in U.S. Pat. No. 5,403,129, issued Apr. 4, 1995, to Steussy. Unfortunately, while the Steussy table has advantages over current systems, it still is deficient in several areas. The principal deficiency in the Steussy table is that even though the table has a stop that rides along a fence, the pivoting nature of the design makes it impossible to provide a measurement function in this plane because the center or zero position of the fence changes with each pivot adjustment. Another deficiency in the Steussy table arises because the table of a drill press typically is mounted to a column; thus, when a height adjustment is made to the table, the table is allowed to rotate around the column, thereby requiring the tool to be changed to recalibrate the table position.